PRECONDITION ANALYSIS IN PROLOG INTERPRETATION.

The authors present an idea called precondition analysis to improve the efficiency of Prolog interpretation. Preconditions are associated with each clause in the program, and the application of a clause as input clause for resolution with a literal is subject to the satisfaction of the respective preconditions by the literal. Such a precondition check makes it possible to identify the failing branches of the SLD-tree, in the proof process, as early as possible without actually encountering the failure. Thus this can be an effective way of pruning the search tree. The authors show how the preconditions can be synthesized automatically by analyzing the program at a preprocessing stage and by analyzing the failures at run time.